Nonwoven fabrics and method for making same



United States Patent O 3,510,390 NONWOVEN FABRICS AND METHOD FOR MAKING SAME Johan A. Bjorksten, Fitchburg, and Robert P. Cox, Madison, Wis., and Risto P. Lappala and Luther L. Yaeger, Houston, Tex., assignors, by mesne assignments, to Bj-orksten Research Laboratories, Inc., Madison, Wis., a corporation of Wisconsin No Drawing. Filed Jan. 30, 1967, Ser. No. 612,368 Int. Cl. D04h 1/54, 1/64; B32b 5/08 US. Cl. 161-150 14 Claims ABSTRACT OF THE DISCLOSURE A nonwoven fabric having a plurality of separate interlaced fiber networks is disclosed such that each fiber network comprises a preselected goup of fibers bonded together at substantially all points of contact with fibers of said group, and substantially free of significant bonding restraint at points of contact with fibers of other networks. Methods are also disclosed in which the fiber group are selectively bonded with solvents, adhesives, and/or heat treatment.

Fabrics may be divided into two general groupings, woven and nonwoven. Woven fabrics may be considered to be any fabric, including knitted fabrics, in which substantially continuous lengths of fibers, filaments or yarns are connected in a generally regular arrangement or pattern. Woven fabrics are usually characterized by good hand and drape characteristics resulting from mobility of the fiber structure. Also, woven fabrics have good strength and dimensional stability. In contrast, nonwoven fabrics are generally in the form of a bat or mat of randomly arranged filaments or fibers, usually of short length, bonded or held together. Nonwoven fabrics are distinguished by a flat sheet-like appearance with a tendency toward boardiness of hand and/ or relatively poor strength. The principal advantage of nonwovens is lower cost. This is due to v the fact that in the preparation of woven fabrics it is necessary to spin and twist fibers into yarns and weave, knit or braid the yarns into fabrics. These operations are slow and expensive and involve the use of many complicated machines and much labor.

Because of the lower cost of nonwovens, there has been considerable work to produce a fabric which has the lower cost of non-woven fabrics, while achieving the properties of woven fabrics. Nonwoven fabrics commonly are made by mixing fibers of staple length and depositing the fibers in a continuous sheet or web. The fibers in web form are then bonded together, for example, by theapplication of an adhesive binder or by mechanically compressing the fibers into contact with one another, etc. The. binder is selected to give good bonding to a variety of different fibers so uniform bonding throughout the bat will be achieved. To obtain a fabric with resonable strength, it is necessary to employ a substantial proportion of the adhesive binder. However, this high concentration of binder produces a fabric which is boardy rather than soft and supple due to the low degree of movement or slip between the individual fibers therein.

To improve the hand of the fabrics, it has been proposed to apply an adhesive binder over only a portion of the surface of the fiber bat. While this procedure reduces the boardiness of the fabric, it is only accomplished by sacrificing strength of the fabric. Also, it has been suggested to employ an adhesive binder which is rubbery or plastic in nature so that extensibility will be achieved through the deformation of the binder at the points of contact between the fibers. This results only in a limited improvement in hand of the fabric. Thus, it has not been 3,510,390 Patented May 5, 1970 possible to successfully emulate characteristics of woven fabrics in nonwovens.

A principal object of the present invention is to provide a new and improved fabric utilizing bonding techniques to hold the fibers or filaments together.

Another object of the invention is to provide a fabric containing fibers which are selectively bonded to fibers of the same type.

A further object of the invention is to provide a novel non-woven fabric with a high degree of movement or slip of the individual fibers.

An additional object of the invention is to provide a nonwoven fabric having improved hand and drape as compared with commercially available nonwoven fabrics.

The fabric of the present invention includes a fiber network comprising a preselected group of fibers bonded to gether with other fibers of the respective group. While fibers of one network are in contact with different fibers of the fabric, the fibers of the network are substantially free of bonding restraint at points of contact with such different fibers. While there may be incidental bonding of fibers of the network with the different fibers of the fabric, the network should be free of any significant restraint from the different fibers due to such incidental bonding. The presence of an independent and separate fiber network within the fabric structure of the invention provides a high degree. of independent movement or slip of fibers of nonwoven fabrics. This gives improved hand and drape to such fabrics without significantly sacrificing strength.

In the same way that the first network is formed, other preselected groups of fibers also may be selectively bonded together without significant bonding to the fibers in the first and remaining networks. Likewise, third, fourth or more independent bonded fiber networks may be formed. Such a structure has a high level of strength since substantially all of the fibers are bonded in one way or another into the structure. However, because the fibers are bonded into a plurality of networks, interlaced but substantially independent of each other, an increase is achieved in the potential slip or movement of one fiber with respect to another. This produces a significant improvement in the aesthetic characteristics of the product For example, the hand is much less boardy, and the visual appearance of the fabric is more pleasing.

The fabrics of the invention may include any of the known fiber materials, either organic or inorganic and natural or synthetic in type. Particularly useful are natural fibers such as cotton, silk and wool, etc.; cellulosic fibers, e.g., cellulose acetate, viscose rayon and the like; polymeric synthetic fibers such as polyolefins, polyesters, polyamides, polyacrylics, polyvinyls, etc.; siliceous materials, for example, glass and vitreous silica; and other fibers, e.g., carbon, metal, ceramic and asbestos; and similar fibers.

The separate fiber networks may be produced in a wide variety of ways and generally are produced by selective treatments of blends of different fibers to produce preferential bonding. Such treatments may be the result of solvent or adhesive effects or polymerization reactions. The particular fibers selected for use in the fabric of the invention will determine the treatment or technique to be used for effecting the bonding of a group of fibers into a separate network within the fabric. Some of the fibers may be tackified or softened through the use of solvents or solvent mixtures, and this may be an acceptamle expedient for the bonding of such fibers. However, if the remaining fibers in the fabric are also softened by the solvent selected, preferential bonding would not be achieved but instead all of the fibers would be bonded together. Also, if the fibers are tackified by the solvent, they would bond not only to like fibers, but also to difierent types of bers in the fabric. This would be unacceptable for the purposes of the invention since a separate network of preselected fibers would not result. Thus, it is important for the purpose of the invention that the technique selected for the formation of each network provide substantially exclusive bonding of a preselected group of fibers without producing significant bonding to other fibers in the fabric.

As an illustration of the invention, a blend of polyamide and cellulose acetate fibers is formed into a bat or mat, and the bat treated with an aqueous ethyl acetate solution or dispersion. This treatment bonds the acetate fibers together into a network but does not produce any significant bonding of the acetate fibers to the polyamide fibers. The bat is then treated with a concentrated solution of calcium chloride in methanol which selectively bonds the polyamide fibers together, but does not bond the polyamide fibers to the cellulose acetate fiber network. In this way, a fabric is produced with two interlaced but separate fiber networks, one being acetate fibers and the second, polyamide fibers. The ethyl acetate advantageously may be added to the calcium chloride-methanol solution and the polyamide-acetate blend subjected to a single treatment with the combination. This results in the simultaneous production of the same independent fiber networks; namely, the cellulose acetate and the polyamide networks, as the successive treatments above.

A solvent mixture may be used in a different way for the sequential treatment of fibers of different types. For example, a blend of solvents may be selected such that the starting mixture acts as a solvent to bond one group of fibers but not the others. Then, one or more components of the solvent mixture is removed, for example, by evaporation of the lower boiling materials with the result that the remaining portion is a solvent which bonds a different group of fibers into a separate network. A mixture of formic acid and dimethyl formamide in particular proportions selectively bonds a blend of polyamide and polyvinyl chloride fibers. The starting mixture bonds the polyamide fibers and after heating to evaporate the formic acid, the remainder of the solvent mixture bonds the polyvinyl chloride fibers.

Another useful technique for the bonding of fibers into a network is the use of adhesive including latices. For example, commercially available urethane latices are water-based resin systems which bond either very well or very poorly depending on the particular type of fiber. Such urethane latices have good adhesion to cotton but poor adhesion to cellulose acetate and would be useful in the selective bonding of cotton in a cotton-acetate blend.

In situations where a suitable solvent for a particular fiber cannot readily be found, an alternative technique may be to precoat the fibers prior to the use of a solvent. The solvent tackifies the coating without attacking the base fiber and thus yields the desired preferential bonding. For example, a polyester-cellulose acetate blend may be preferentially bonded simply and conveniently by first coating the polyester fibers with a polyamide coating and thereafter treating a blend of polyamide-coated polyester fibers and cellulose acetate fibers with a solution of ethyl acetate, calcium chloride and methanol as described above. The polyamide coating on the polyester fiber is tackified which bonds these fibers into one network, while the acetate fibers are bonded into a separate network.

A further expedient for producing selectively bonded fiber networks is the use of catalyzed coatings in which one material is applied to a group of fibers and a second material which reacts with the first material is applied to a second group of fibers. The application of these reactants is performed prior to the blending of the two groups of fibers with fibers of a different type or types. Upon heating the blend, a reaction takes place between the two groups of coated fibers with the result that bonding is achieved. However, the fibers which have not been coated with reactants remain unbonded and can be bonded into separate networks using different techniques. For example, a group of polyamide fibers may be coated with a polyethylene glycol while a group of polyester fibers is coated with tolyl diisocyanate. Upon heating, fusion and reaction takes place at the points of contacts between the polyamide and polyester fibers with the result that a polyamide-polyester fiber network is produced, which is more flexible than a conventional one fiber network. This is due to the absence of any significant polyamide to polyamide and polyester to polyester bonding so that movement and slip of the fibers with respect to each other is possible. Thus, with a blend of these twogroups of fibers with another fiber such as a polyolefin, which is bonded by a different system, a loose polyamide-polyester fiber network and a polyolefins network result.

Heat may be employed to bond certain fibers. In a blend of heat bondable fibers with solvent bondable fibers, a network of the solvent bondable fibers may be formed in the first stage of treatment and next a network of the heat bondable fibers may be produced by subjecting the blend to an elevated temperature above the soften point of the latter fibers.

The following is a listing of specific bonding techniques which are useful with particular fibers:

Cellulose acetate fibers.-Ketones; esters; phenoxy resin solutions.

Viscose rayon fibers.--60% aqueous zinc chloride; hydrophilic fibrous cellulose ether, e.g., carboxyethyl cellulose.

Cotton fibers.Urethane latices; plasticized polyvinyl butyral; phenoxy resin solutions.

Wool fibers.Urethane latices; basic solutions of basic resins; surface reduction and subsequent reaction.

Polyvinyl fibers.-Ketones; esters; heat.

Polyamide fibers.Calcium chloride-methanol (a solvating electrolytic-low MW primary alcohol); formic acid solutions with dimethyl formamide; formic acid followed by dichloromethane; plasticized polyvinyl butyral; phenol; trifluoroethanol; methacrylate copolymer adhesives.

Polyester fibers.ln situ formed polyurethanes; plasticized polyvinyl butyral; polymethyl methacrylate solutions; urethane latices; solvent-soluble polyesters; epoxy resins; phenoxy resin solutions.

Polyolefin fibers.-Heat; methacrylate copolymer adhesives; decalin or dichlorobenzene.

Polyacrylic fibers.--Phenoxy resin solutions; ethylene and propylene carbonate; gamma valerolactone; aqueous calcium thiocyanate.

Glass fibers.Low melting glasses; aluminum phosphate solutions; silane finish-epoxy resins; difunctional halosilanes.

Although the above bonding techniques are useful for particular fibers, in selecting bonding techniques for a blend of different type fibers, the technique employed to bond one fiber into a network must not affect the other fibers in the blend. If the bonding technique has an effect on more than one type of fiber it will not be possible to produce the unique fabrics of the invention with the separate but interlaced bonded fiber networks. If the effect of the bonding technique is not known, a simple test may be performed by placing yarns of each type in contact with one another and attempting the bonding at the point of contact. Advantageously, this test is conducted with yarns of considerable length which may be stretched crosswise on a simple hand weaving loom. The force required to draw one fiber from contact with another will indicate the kind of bonding obtained and between which fibers to facilitate selection of proper fiber systems and bonding techniques.

In the formation of the nonwoven fabrics of the present invention conventional bat and web forming procedures may be utilized. Usually, fibers of staple length are blended and mechanically carded. The carded fibers are formed into a bat such as by distributing the fibers over the surface of a screen and compressing the deposited fibers into a mat or web of uniform density. While the invention is particularly useful for fibers of stable length, it will be apparent that the selective bonding techniques of the invention also are useful for other types of fabrics in which bonding is desirable. For example, systems are available for the deposition of continuous filaments in a zig zag path with the application of additional filaments in a different pattern over the first. The points of contact are then bonded to form a nonwoven fabricr'of continuous filaments. The invention also is useful in the selective bonding of woven or knitted fabrics. For example, multifiber woven fabrics may be combined and bonded together using a bonding technique which selectively bonds a preselected group of fibers in one fabric to a preselected group of fibers in another fabric.

The invention will be described in greater detail with reference to the following examples. The examples are intended to illustrate various embodiments of the invention and not to limit the scope thereof. In the examples, parts and percentages are by weight.

EXAMPLE I A polyamide resin is dissolved in a saturated solution of calcium chloride in methanol at about 90 F. and then ethyl acetate is added to produce a solution containing about 2.5% polyamide and 5% ethyl acetate.

A bat formed by blending staple length yellow polyamide fibers, pink cellulose acetate fibers and white cotton and having an uncompressed thickness of about A inch and a weight of about 1 /2 ounces per square yard, is saturated with the above solution while the bat is positioned on a metal screen. The excess solution is squeezed from the bat and the bat allowed to dry. The bat is rinsed with methanol, squeezed to remove excess liquid, rinsed with water, again squeezed and air dried. Next, the bat is saturated with a commercially available urethane latex (sold by Wyandotte Chemical Company as P-204A Latex) which has been diluted to four times its volume with water. The latex-coated bat is then squeezed, rinsed with water and dried.

The resulting bonded fabric having a thickness of about inch has good hand without boardiness or harshness. In manipulation of the fabric by pulling and squeezing, a high degree of slip and movement of the fibers with respect to each other is observable. Examination under a low power microscope shows bonding of the yellow polyamide fibers at points of contact therebetween to form a network. Likewise, the pink acetate fibers are bonded together into a network and the white cotton into a separate network. No apparent bonding takes place at points where the polyamide, acetate and cotton fibers contact one another.

A comparison of the fabric with commercially available non-woven fabrics of the same fiber blend shows that the fabric prepared according to the above procedure has a softer, more supple hand than the commercial fabrics and approaching that of commercial woven and knitted fabrics of the same blend. Also, the fabric of the invention exhibits more slip between the fibers with a tear strength of the same order of magnitude as the com mercial non-woven fabrics. Treatment of the fabric with commercial detergents and dry cleaning solvents does not significantly alter the strength or hand of the fabric.

EXAMPLE II A blend of blue polyester fiber and yellow polyamide fiber is prepared and formed into a 'bat similar to that of Example I. The bat is saturated with a phenoxy resin emulsion. The emulsion is prepared by mixing 50 parts of a phenoxy resin solution (sold by Union Carbide Chemicals under the tradename Bakelite Phenoxy Resin PKHS as a 46% solids solution in a mixture of toluol and methylethyl ketone) with 2.5 parts of a nonionic surfactant sold by Atlas Chemical Industries as Span 85 and 2.5 parts of nonionic surfactant sold by Atlas Chemical Industries as Tween 80. After thoroughly mixing the above, the mixture is added slowly to 100 parts of water which is being agitated with a high speed stirrer to form the emulsion used to treat the bat.

The saturated bat is rinsed with water and dried. The bat then is treated with a 2.5% solution of polyamide in a saturated solution of calcium chloride in methanol at about F. The bat is again squeezed to remove excess liquid, rinsed with methanol, squeezed again, washed with Water and air dried.

The resulting fabric has a soft supple hand and a high degree of slip between the separate polyamide and polyester fiber networks as observable in microscopic examination. The fabric shows the same superiorities over commercially available nonwoven fabrics as does the fabric of Example I both before and after laundering or dry cleanmg.

EXAMPLE III A blend of gray acrylic fiber and black viscose fiber is prepared and formed into a bat similar to that of Examples I and II. The bat is saturated with a 25% aqueous ethylene carbonate solution and thereafter rinsed with Water and dried. The bat is then treated with the diluted aqueous urethane latex employed in Example I. The bat is again squeezed to remove excess liquid, rinsed with water and air dried.

The fabric has a soft hand and a high degree of fiber movement. The presence of separate acrylic fiber and viscose fiber networks is observable in microscopic examination of the fabric. The hand and slip characteristics are retained even after laundering or dry cleaning.

EXAMPLE IV Blue polyester fibers are blended with white cotton fibers to form a bat, and the bat is immersed in a solution containing about 1% of a vinyl silane finish (sold by Union Carbide Silicones Division as A-l72) and about 0.02% morpholine. The excess solution is squeezed from the bat and while the fibers are still damp, a diallyl phthalate prepolymer in powder form (sold by F-MC Corporation as Dapon) is sprinkled onto the fibers. The excess powder is shaken from the bat, and the bat is then sprayed with a hexane solution containing about 2 of tertiary butyl peroctoate. The resulting coated bat is compressed to provide intimate contact between the fibers while being heated to a temperature of about 250 F.

The cotton fibers are bonded according to the procedure of Example I using the P-204A urethane latex. The bat is rinsed with water and air dried.

Microscopic examination of the fabric shows interlaced separate networks of the polyester fibers and the cotton fibers. No bonding is apparent at points where the polyester and cotton fibers contact each other. The fabric has a soft hand even after laundering or dry cleaning.

EXAMPLE V Staple length yellow polyamide fibers are coated with a solution prepared by combining about 8 parts of a commercially available branched multifunctional polyester coating material sold by Mobay Chemical Company as Multron R-12, 8 parts of a 36% solids polymethyl methacrylate solution in cellulose acetate sold by Rohm & Haas Company as Acryloid A-10 and one part of a diisooctylphthalate plasticizer sold by Union Carbide Chemicals as Flexol 3-GH. In the same way, blue polyester fibers are treated with a solution containing about 8 parts of a polyisocyanate sold by Mobay Chemical Company as Mondur CB-75, 8 parts of Acryloid A-l0 (above), 2 parts of Flexol 3GH (above), 0.1 part dibutyl tin dilaurate and 0.3 part of triethylamine. The resulting coated polyamide and polyester fibers are blended with white cotton and formed into a bat which is heated in an oven at a temperature of about C. for about 15 minutes.

The fabric is then washed with a commercially available detergent solution using agitation, rinsed with water and allowed to dry. Thereafter, the bat is treated with the P-204A Latex used in Example I and again washed and dried.

The fabric has a soft hand and good strength. Microscopic examination shows substantially all of the bonding of the polyamide and polyester fibers is cross bonding, rather than polyamide-to-polyamide or polyester-to-polyester bonding. The cotton is bonded into a separate network.

Manipulation of the fabric sample shows a high level of slippage between the fibers as compared with commercial nonwoven fabrics. The fabric shows the same superiorities as the fabrics of the invention prepared in Examples I and II.

EXAMPLE VI Blue polyester fibers are coated with a thin film of cellulose acetate resin by immersing the polyester fibers in a cellulose acetate solution in acetone. After allowing the polyester fibers to dry, they are blended with gray acrylic fibers to form a bat. The bat is saturated with a solvent blend composed,.by volume, of 9 parts of a 62% calcium thiocyanate aqueous solution and 4 parts of acetone. The bat and solvent are heated to evaporate the acetone and the bat is then thoroughly rinsed with water and air dried. Initially, a network of the cellulose acetate coated-polyester fibers is formed and as the acetone is evaporated from the solvent blend, a network of the acrylic fibers is formed. No cross bonding between the polyester and the acrylic fibers is observable even upon microscopic examination.

The fabric has a supple-hand and a high degree of movement between the separate polyester and acrylic fiber networks which is retained even after laundering or dry cleaning.

In the same way the bonding techniques listed above may be utilized to bond other fiber combinations to form the novel fabrics of the invention. These fabrics have soft supple hand and good strength similar to the fabrics of the above examples.

It is apparent from the above description and examples that the present invention provides a novel fabric. Furthermore, the fabric of the invention has improved hand and drape with good strength. According to the invention, these improved results are attained through the novel arrangement of a preselected group of fibers into a fiber network which heretofore was not known.

That which is claimed is:

1. A nonwoven fabric including a plurality of separate interlaced fiber networks with each network comprising a preselected group of fibers bonded together at substantially all points of contact with fibers of said group, and substantially free of significant bonding restraint at points of contact with fibers of other networks.

2. A fabric according to claim 1 in which one of said networks comprises synthetic polymeric fibers.

3. A fabric according to claim 1 in which one of said networks comprises polyamide fibers.

4. A nonwoven fabric according to claim 1 in which said fibers are of staple length.

5. A nonwoven fabric according to claim 1 in which said fabric comprises networks of polyamide, cellulose acetate and cotton fibers.

6. A nonwoven fabric according to claim 1 in which said fabric comprises networks of polyamide and polyester fibers.

7. A method of forming a nonwoven fabric including a bat of plural separately interlaced fiber networks which comprises bonding a first preselected group of fibers into a first fiber network having the fibers bonded together at substantially all points of contact between the fibers of said network, bonding a second preselected group of fibers into a second fiber network having the fibers bonded together at substantially all points of contact between the fibers of said second network, said second network of fibers being interlaced through said first network of fibers without any significant bonding restraint between said networks in said bat.

8. A method according to claim 7 in which one of said preselected groups of fibers is subjected to at least one solvent for said fibers to bond them into a fiber network.

9. A method according to claim 7 in which one of said preselected groups of fibers is treated with at least one adhesive material to bond said fibers into a fiber network.

10. A method according to claim 7 in which one of the preselected groups of fibers is formed of two different sets of precoated fibers, a first set of fibers being coated with a polyalkylene glycol and a second set of fibers being coated with an isocyanate, and said bat including said first and second preselected groups of fibers is heated to bond said first and second sets of precoated fibers to form a fiber network without any significant bonding restraint from the remaining fibers in said bat.

11. A method according to claim 7 in which at least two preselected groups of fibers are blended to form a bat, in which at least one group of fibers comprises polyamide fibers and in which said bat is subjected to a solvent mixture comprising a concentrated solution of calcium chloride in methanol to bond the polyamide fibers into a separate network.

12. A method according to claim 11 in which said product consists essentially of polyamide, cellulose acetate and cotton fibers, and said bat is subjected to ethyl acetate, calcium chloride, methanol and latex to form separate networks of the polyamide, cellulose acetate and cotton fibers respectively, so that networks are interlaced without any considerable bonding restraint between said networks.

13. A method according to claim 12 in which the respective networks are formed sequentially.

14. A method according to claim 12 in which the polyamide fiber and cellulose acetate fiber networks are formed substantially simultaneously.

References Cited UNITED STATES PATENTS 2,543,101 2/1951 Francis 161150 2,900,291 8/1959 OConnell l61150 3,395,060 7/1968 Guldner 161-150 ROBERT F. BURNETT, Primary Examiner W. W. SCHWARZE, Assistant Examiner US. Cl. X.R. 

